[mutter] build: Use Xwayland pkg-config if available

[Marge Bot <marge-bot src gnome org>]

commit 533e6768dace01c7ef7d4eaf122e30b860f46ba5
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Tue Dec 15 10:19:05 2020 +0100

    build: Use Xwayland pkg-config if available
    
    Xwayland in its main development branch now provides a pkg-config file
    which can be used to determine Xwayland installation path and various
    options enabled at build time.
    
    Change mutter build system to optionally use that mechanism if
    available. If not (as with Xwayland from the current stable branch),
    keep the fallback mechanisms (basically search for the Xwayland and parse
    its command line options to determine if initfd is available).
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1635>

 meson.build | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)
---
diff --git a/meson.build b/meson.build
index 782a8e3640..c9d50514e7 100644
--- a/meson.build
+++ b/meson.build
@@ -392,9 +392,15 @@ endif
 
 have_xwayland_initfd = false
 if have_wayland
+  xwayland_dep = dependency('xwayland', required: false)
+
   xwayland_path = get_option('xwayland_path')
   if xwayland_path == ''
-    xwayland_path = find_program('Xwayland').path()
+    if xwayland_dep.found()
+      xwayland_path = xwayland_dep.get_pkgconfig_variable('xwayland')
+    else
+      xwayland_path = find_program('Xwayland').path()
+    endif
   endif
   cdata.set_quoted('XWAYLAND_PATH', xwayland_path)
 
@@ -409,12 +415,18 @@ if have_wayland
 
   # For Xwayland -initfd usage
   use_initfd = get_option('xwayland_initfd')
-  xwayland_options = run_command(xwayland_path, '-help')
+  if xwayland_dep.found()
+    xwayland_supports_initfd = xwayland_dep.get_pkgconfig_variable('have_initfd') == 'true'
+  else
+    xwayland_options = run_command(xwayland_path, '-help')
+    xwayland_supports_initfd = xwayland_options.stderr().contains('-initfd')
+  endif
+
   if use_initfd.auto()
-    have_xwayland_initfd = xwayland_options.stderr().contains('-initfd')
+    have_xwayland_initfd = xwayland_supports_initfd
   else
     have_xwayland_initfd = use_initfd.enabled()
-    if have_xwayland_initfd and not xwayland_options.stderr().contains('-initfd')
+    if have_xwayland_initfd and not xwayland_supports_initfd
       error('XWayland -initfd support requested but not available')
     endif
   endif